How does a fur seal mother recognize the voice of her pup? An experimental study of Arctocephalus tropicalis.

In the subantarctic fur seal Arctocephalus tropicalis, mothers leave their pups during the rearing period to make long and frequent feeding trips to sea. When a female returns from the ocean, she has to find her pup among several hundred others. Taking into account both spectral and temporal domains, we investigated the individual vocal signature occurring in the 'female attraction call' used by pups to attract their mother. We calculated the intra- and inter-individual variability for each measured acoustic cue to isolate those likely to contain information about individual identity. We then tested these cues in playback experiments. Our results show that a female pays particular attention to the lower part of the signal spectrum, the fundamental frequency accompanied by its first two harmonics being sufficient to elicit reliable recognition. The spectral energy distribution is also important for the recognition process. Of the temporal features, frequency modulation appears to be a key component for individual recognition, whereas amplitude modulation is not implicated in the identification of the pup's voice by its mother. We discuss these results with respect to the constraints imposed on fur seals by a colonial way of life.